L18 - Visual Cortex 2 (TV)

Question 1

List 3 neuroanatomical tracing techniques

Answer 1

1) Radioactive amino acids-Inject into one eye and determine labeling in cortex of ocular DOMINANCE columns

2) 2-Deoxyglucose (2DG)-ONLY TAKEN UP BY ACTIVE CELLS - Injecting glucose analogue (C14 is radioactive - allows us to identify cells that are active) taken up after visual stimulation BUT only by the cells in which the ORIENTATION it was showed in
* Layer 4C is labelled because the cells are not orientation selective - infragranular layers 5 and 6 have orientation columns

3) Cytochrome oxidase levels - Mitochondrial enzyme (High basal metabolic rate - layer 4 and blobs). Cells that are more active have more cytochrome oxidase. This can be shown using radioactive proline injections.

Question 2

Which layer is not orientation selective?

Answer 2

Layer 4C

Question 3

Cytochrome oxidase staining in macaque V1 shows? V2 shows?

Answer 3

V1 - Blobs
V2 - Stripes (thick and thin stripes)

Cells more active seem to be more clustered compared to the rest

Question 4

Where does cytochrome oxidase blobs coincide with in regards to ocular dominance columns?

Answer 4

The centre of the columns

*You rarely find them at the border of two columns

Question 5

How may one attempt to see the relationship between ocular dominance and orientation columns?(addresses 3rd dot point of learning objectives)

Answer 5

Inject radioactive amino acids (ocular dominance columns) then inject 2-deoxyglucose (orientation columns)

Question 6

Where do all orientation domains seem to converge?

Answer 6

At the pinwheel centre

Question 7

List 3 optical imaging techniques

Answer 7

1) Voltage-sensitive dyes - The dye is poured onto the cortex’s surface, which sticks to the cell membranes and fluoresces (changes colour) when the cells depolarize aka are active. Good temporal resolution BUT dyes are toxic hence cannot record for long time
2) Intrinsic signals- Expose the cortex, use a camera and shine a particular light to capture the reflectance changes from intrinsic signals from active tissue. There are also light scattering changes from ion and water movement (blood volume) and the colour changes in oxygenation of blood - in deoxyhaemoglobin and oxyhaemoglobin

Poor temporal resolution. HOWEVER the spatial resolution was not good enough to know the properties of cells at pinwheel centres - their orientation selectivity and spatial order

3) 2-photon calcium imaging - oregon green dye gets trapped in cells and fluoresces durings Ca 2+ influx. It helps in mapping neuronal activity at single-cell resolution and in 3D